Exposure to sunlight and other sources of ultraviolet radiation is known to cause degradation of a wide variety of materials, especially polymeric materials. For example, polymeric materials such as plastics often discolor and/or become brittle as a result of prolonged exposure to ultraviolet light. Accordingly, a large body of art has been developed directed towards materials such as ultraviolet light absorbers and stabilizers which are capable of inhibiting such degradation.
A class of materials known to be ultraviolet light absorbers are triazines. Triazine ultraviolet light absorbers are a class of compounds which have at least one 2-hydroxyphenyl substituent on the 1,3,5-triazine ring. ##STR1##
Trisaryltriazine ultraviolet light absorbers are compounds which have aromatic substituents at the 2-, 4- and 6-positions of the 1,3,5-triazine ring, and in which at least one of the aromatic rings has a hydroxyl substituent at the ortho position. These aromatic rings may contain other substituents or may be fused polyaromatics. In general this class of compounds is well known in the art. Disclosures of a number of such trisaryl-1,3,5-triazines, as well as processes for preparing and uses thereof, can be found in the following publications, all of which are incorporated by reference as if fully set forth herein: U.S. Pat. Nos. 3,118,887, 3,242,175, 3,244,708, 3,249,608, 3,268,474, 3,423,360, 4,619,956, 4,740,542, 5,084,570, 5,288,778, 5,461,151, 5,476,937, 5,478,935, 5,543,518, 5,545,836, 5,591,850, and 5,597,854, British patent 1,033,387, Swiss patents 480,091 and 484,695, European patent applications 0,444,323 and 0,649,841, and PCT applications WO94/05645 and WO96/28431.
A commonly used class of trisaryl-1,3,5-triazine ultraviolet light absorbers is based on 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazines. In these compounds two non-phenolic aromatic groups and one phenolic aromatic group are attached to the 1,3,5-triazine. The phenolic aromatic group is derived from resorcinol. ##STR2##
Of this class of compounds, a number of commercial examples exist in which the para-hydroxyl group of the phenolic ring is functionalized and the non-phenolic aromatic rings are either unsubstituted phenyl, as in TINUVIN 1577 or meta-xylyl, as in CYASORB UV-1164, CYASORB UV-1164L and TINUVIN 400. These ultraviolet light absorbers exhibit high inherent light stability and permanence as compared to other classes of ultraviolet light absorbers such as benzotriazoles and benzophenones. ##STR3##
Several approaches to the production of 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazines have been reported in the literature. For example, H. Brunetti and C. E. Luethi, Helvetica Chimica Acta, vol. 55, pages 1566-1595 (1972), and S. Tanimoto and M. Yamagata, Senryo to Yakahin, vol. 40 (12), pages 325-339 (1995).
The majority of the approaches are based on cyanuric chloride, a readily available and inexpensive starting material. Resorcinol is known to be much more reactive than meta-xylene toward cyanuric chloride, and in Y. Horikoshi et al, Nippon Kagaku Kaishi (3), pages 530-535, (1974), CA 81:152177 it has been reported to form only the bis-resorcinol-monochloro-triazine and/or trisresorcinol triazine even when cyanuric chloride to resorcinol were used in equimolar ratios. U.S. Pat No. 3,270,016 describes the formation of bis-resorcinol monochloro triazine in good yield by reacting cyanuric chloride and resorcinol at about equimolar ratio at room temperature for 10 hours, with no mention of the formation of the mono-resorcinol bischloro triazine. Further, German patent application DE 1,169,947 or GB 884802 as mentioned in U.S. Pat No. 5,726,310, describes uncontrolled exothermic reaction when cyanuric chloride, meta-xylene and aluminum chloride are simultaneously introduced.
In one method, shown below, cyanuric chloride is reacted with aromatic compounds, such as meta-xylene, in the presence of aluminum chloride. The reaction produces a monochloro-bisaryl-1,3,5-triazine, which is then reacted with resorcinol in a second step to form a 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine. This process contains several limitations which relate to the first step of the reaction, namely that the first step is not selective and leads to a mixture of all of the possible products, plus unreacted cyanuric chloride. This means that the desired monochloro-bisaryl-1,3,5-triazine must be separated from the reaction mixture before the second reaction step takes place. Another disadvantage is that the first reaction step is not generally applicable to all aromatic compounds. It is well known in the literature that the use of this process gives a useful yield of the desired monochloro-bisaryl-1,3,5-triazine intermediate only when meta-xylene is the aromatic reactant. With other aromatic species, an inseparable mixture of all possible products is formed, and no selectivity for the desired monochloro-bisaryl-1,3,5-triazine is seen. See Brunelli, page 1575. For the meta-xylene based product, an improved process has recently been disclosed in U.S. Pat. No. 5,726,310, in which the monochloro-bis(2,4-dimethylphenyl)-1,3,5-triazine intermediate produced in the first reaction step is not isolated, but is further reacted with resorcinol in a one-pot, two-step process. This process contains the disadvantage not only of its being applicable only to meta-xylene, but also that it is a two-step process. ##STR4##
In another approach, shown below, cyanuric chloride is reacted with an aryl magnesium halide to prepare a monochloro bisaryl triazine in the first step. The substituted triazine intermediate is isolated and subsequently reacted with resorcinol to produce a 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine. It has been reported that this approach is not selective for the monochloro-bisaryl triazine, for example, Brunetti, page 1575. However, modifications with better results have been reported, as in U.S. Pat No. 5,438,138. While this approach is generally applicable to many aromatic species, it has the disadvantages of being unsuitable for industrial scale production due to the use of a highly reactive Grignard reagent, and uneconomical due to the special precautions associated with the use of Grignard reagents, and the cost of the raw materials used in these compounds. ##STR5##
Alternative approaches have been developed to address the selectivity problem. In one approach, shown below, cyanuric chloride is first reacted with one equivalent of an alcohol to produce, with high selectivity, a monoalkoxy-bischlorotriazine. This substituted triazine is then reacted in a second step with aromatics in the presence of aluminum chloride to prepare monoalkoxy/hydroxy-bisaryltriazines. These intermediates are then converted to monochloro-bisaryltriazines by reaction with thionyl chloride or phosphorus pentachloride. The monochloro-bisaryltriazines are finally reacted with resorcinol in a fourth step to prepare the desired 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine. This approach can be applied generally to aromatic species, and the desired product is formed with selectivity, but the addition of several steps in the synthesis makes this process economically unattractive. ##STR6##
A similar approach is described in U.S. Pat. No. 5,106,972 and U.S. Pat. No. 5,084,570, and is shown below. Cyanuric chloride is first reacted with one equivalent of alkanethiol instead of alcohol. The remaining steps are the same as those described in the previous example. As before, the disadvantage of this approach lies in the additional steps of the synthesis. ##STR7##
A modification of this approach is disclosed in Japanese patent application 09-059,263. In this process, cyanuric chloride is first reacted with one equivalent of a substituted phenol, such as para-chlorophenol, in the presence of aluminum chloride to produce the oxygen-linked mono-phenoxy derivative of cyanuric chloride. This intermediate is subsequently reacted with an aromatic, such as meta-xylene, and aluminum chloride to prepare 2-monophenoxy-4,6-bisaryl-1,3,5-triazine, which is subsequently reacted with resorcinol and aluminum chloride in a third step to produce a 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine. This one-pot, three-step process claims an improved yield of the desired product. However, this method has the disadvantage of the need to use para chlorophenol, a toxic chemical, and the need to remove it from the desired product. ##STR8##
A further approach to the production of 2-chloro-4,6-bisaryl-1,3,5-triazines is disclosed in European patent application 0,497,734. This process involves reacting benzamidine hydrochloride with a chloroformate and dimerizing the product. The resultant 2-hydroxy-4,6-bisaryl-1,3,5-triazine is converted to 2-chloro-4,6-bisaryl-1,3,5-triazine by treatment with thionyl chloride, and finally reaction with resorcinol to produce the 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazine. This method also has the disadvantage of using para-chlorophenol, a toxic chemical. Further the multi-step synthesis renders the process uneconomical for industrial use. ##STR9##
In addition to the approaches described above, other approaches exist which utilize benzonitriles or benzamidines as the starting material. The use of 2,4-dihydroxybenzaldehyde, phenyl (or alkyl) 2,4-dihydroxybenzoates and 2-aryl-1,3-benzoxazine-4-ones is shown below, and is disclosed in, for example, U.S. Pat. Nos. 5,705,643 and 5,478,935 and PCT application WO96/28431. These approaches have the disadvantages of the starting materials being expensive, and the possible need for additional synthetic steps in the preparation. ##STR10## ##STR11## ##STR12##
It can be seen that a need exists for a novel method of production of 2-(2,4-dihydroxyphenyl)-4,6-bisaryl-1,3,5-triazines which is highly selective, economical, having minimal synthetic steps and need for isolation of the intermediate, and demonstrates improved safety to the chemist and to the environment. It is the object of this invention to provide such a novel method of production.